This invention relates to a novel vessel or envelope structure which is adapted for use in the manufacture of cathode ray tubes and the like. More particularly the invention relates to a color television tube which sustains itself against very low internal pressure.
In FIG. 1, a prior art color television tube 10 is illustrated schematically. A panel 11, a funnel 12 and a neck 13 are each formed and fused together in a conventional manner. A pin and gun support 14 is inserted in an open end 15 of the neck 13 and sealed therealong. The entire tube 10 is evacuated in a conventional manner and one of various types of implosion protection devices, (e.g. tension or "T" band 16), is compressively disposed about the perimeter of the panel 11 in one of various ways known in the art. A force f represents a destructive impact on the panel 11 and the T band 16 exerts a radial force on the panel 11 in order to reduce the propagation of cracks therein caused by the destructive force f so that the tube 10 slowly devacuates in a manner which will prevent implosion.
Recent developments in the picture tube art have permitted manufacturers to increase the size of TV picture tubes substantially. As the size of television tubes becomes larger, the size, strength, and complexity of the T band arrangement must be greatly increased. For example, a test conducted by Underwriters' Laboratories Inc. subjects the frontal portion of the panel 11 to an impact of about 15 foot pounds delivered by a five pound missile. The amount of energy dissipated by the panel 11 is sufficient to destroy the tube so that glass fragmentation can be observed. Because of the nature of the test, it is necessary to design implosion protection systems to insure successful results should an implosion occur during normal use. This design requirement becomes increasingly difficult with the larger tubes since the evacuated space within the tube 10 and the stresses on the panel face 11 are progressively increased by the larger surface area exposed against the partial pressure of the tube.
In a copending application of Gehl et al., U.S. Ser. No. 029,555, filed the same date as the present disclosure and assigned to Corning Glass Works, the assignee herein, a stress relief notch molded into the funnel portion of the tube is disclosed. For reasons set forth in said disclosure, the position of the notch is preferably located in the funnel near the yoke reference line. Such preference is based upon reasons of safety, i.e. the glass is sufficiently thick to render the tube stable during processing and use. The present invention takes Gehl et al. a step further and suggests that a stress concentrating notch should be located in a zone of maximum stress concentration arising from the impact and have a controlled surface discontinuity to enhance crack off reliability.
The present invention has been made in order to supplement the conventional TV implosion protection device, in such a way that, a reliable outgassing or devacuation of the tube will occur without the necessity of increasing the hardware required for the conventional implosion protection.